ErbB3 (also known as HER3) is a member of the ErbB/HER family of receptor tyrosine kinases (RTKs). Other members of this family include EGFR (also known as ErbB1 or HER1), ErbB2 (also known as HER2 or Neu), and HER4. ErbB receptors regulate cell proliferation, survival and differentiation by activating intracellular signaling cascades that lead to alterations in gene expression.
ErbB receptors are activated by the formation of either homo- or heterodimers. For example, when ErbB3 is co-expressed with ErbB2, an active heterodimeric signaling complex is formed. ErbB3 dimer formation is promoted by its ligand binding. Neuregulin 1 (NRG1) is the primary ligand for ErbB3 that promotes homo- or heterodimerization of the receptor.
ErbB3 has been found to be overexpressed in various cancer types, including breast, gastrointestinal, and pancreatic cancers. Anti-ErbB3 antibodies have been shown to inhibit the growth of several human tumor cell lines in mouse xenografts models. Anti-ErbB3 antibodies are mentioned in, e.g., U.S. Pat. No. 5,480,968; U.S. Pat. No. 5,968,511; US 2004/0197332; U.S. Pat. No. 7,332,580; U.S. Pat. No. 7,705,130; and U.S. Pat. No. 7,846,440. Nonetheless, there is a need in the art for novel ErbB3 antagonists, such as anti-ErbB3 antibodies, for the treatment of cancer and other related disorders.